Add email tag

README.md

@@ -133,6 +133,12 @@ You set the validation rules following the "validate:" tag according to the rule
 | numeric           | Check whether value is numeric or not              |
 | uppercase         | Check whether value is uppercase or not           |
 
+#### Format
+
+| Tag Name          | Description                                       |
+|-------------------|---------------------------------------------------|
+| email             | Check whether value is an email address or not     |
+
 #### Comparisons
 
 | Tag Name          | Description                                       |

csv_test.go

@@ -528,4 +528,41 @@ ABC
 			}
 		}
 	})
+
+	t.Run("validate email", func(t *testing.T) {
+		t.Parallel()
+
+		input := `email
+simple@example.com
+very.common@example.com
+disposable.style.email.with+symbol@example.com
+user.name+tag+sorting@example.com
+admin@mailserver1
+badあ@example.com
+`
+
+		c, err := NewCSV(bytes.NewBufferString(input))
+		if err != nil {
+			t.Fatal(err)
+		}
+
+		type email struct {
+			Email string `validate:"email"`
+		}
+
+		emails := make([]email, 0)
+		errs := c.Decode(&emails)
+		for i, err := range errs {
+			switch i {
+			case 0:
+				if err.Error() != "line:6 column email: target is not a valid email address: value=admin@mailserver1" {
+					t.Errorf("CSV.Decode() got errors: %v", err)
+				}
+			case 1:
+				if err.Error() != "line:7 column email: target is not a valid email address: value=badあ@example.com" {
+					t.Errorf("CSV.Decode() got errors: %v", err)
+				}
+			}
+		}
+	})
 }

errors.go

@@ -96,4 +96,6 @@ var (
 	ErrUppercaseID = "ErrUppercase"
 	// ErrASCIIID is the error ID used when the target is not an ASCII character.
 	ErrASCIIID = "ErrASCII"
+	// ErrEmailID is the error ID used when the target is not an email.
+	ErrEmailID = "ErrEmail"
 )

i18n/en.yaml

@@ -66,3 +66,6 @@
 
 - id: "ErrASCII"
   translation: "target is not an ASCII character"
+
+- id: "ErrEmail"
+  translation: "target is not a valid email address"

i18n/ja.yaml

@@ -72,3 +72,6 @@
 
 - id: "ErrASCII"
   translation: "値がASCII文字ではありません"
+
+- id: "ErrEmail"
+  translation: "値がメールアドレスではありません"

i18n/ru.yaml

@@ -66,3 +66,6 @@
 
 - id: "ErrASCII"
   translation: "целевое значение не является ASCII символом"
+
+- id: "ErrEmail"
+  translation: "целевое значение не является адресом электронной почты"

parser.go

@@ -133,6 +133,8 @@ func (c *CSV) parseValidateTag(tags string) (validators, error) {
 			validatorList = append(validatorList, newUppercaseValidator())
 		case strings.HasPrefix(t, asciiTagValue.String()):
 			validatorList = append(validatorList, newASCIIValidator())
+		case strings.HasPrefix(t, emailTagValue.String()):
+			validatorList = append(validatorList, newEmailValidator())
 		}
 	}
 	return validatorList, nil

tag.go

@@ -48,6 +48,8 @@ const (
 	uppercaseTagValue tagValue = "uppercase"
 	// asciiTagValue is the struct tag name for ascii fields.
 	asciiTagValue tagValue = "ascii"
+	// emailTagValue is the struct tag name for email fields.
+	emailTagValue tagValue = "email"
 )
 
 // String returns the string representation of the tag.

validation.go

@@ -2,6 +2,7 @@ package csv
 
 import (
 	"fmt"
+	"regexp"
 	"strconv"
 	"strings"
 
@@ -461,15 +462,43 @@ func newASCIIValidator() *asciiValidator {
 
 // Do validates the target is an ASCII string.
 func (a *asciiValidator) Do(localizer *i18n.Localizer, target any) error {
+	const maxASCII = 127
+
 	v, ok := target.(string)
 	if !ok {
 		return NewError(localizer, ErrASCIIID, fmt.Sprintf("value=%v", target))
 	}
 
 	for _, r := range v {
-		if r > 127 {
+		if r > maxASCII {
 			return NewError(localizer, ErrASCIIID, fmt.Sprintf("value=%v", target))
 		}
 	}
 	return nil
 }
+
+// emailValidator is a struct that contains the validation rules for an email column.
+type emailValidator struct {
+	regexp *regexp.Regexp
+}
+
+// newEmailValidator returns a new emailValidator.
+func newEmailValidator() *emailValidator {
+	const emailRegexPattern = `^[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}$`
+	return &emailValidator{
+		regexp: regexp.MustCompile(emailRegexPattern),
+	}
+}
+
+// Do validates the target is an email.
+func (e *emailValidator) Do(localizer *i18n.Localizer, target any) error {
+	v, ok := target.(string)
+	if !ok {
+		return NewError(localizer, ErrEmailID, fmt.Sprintf("value=%v", target))
+	}
+
+	if !e.regexp.MatchString(v) {
+		return NewError(localizer, ErrEmailID, fmt.Sprintf("value=%v", target))
+	}
+	return nil
+}